<html><head></head><body><p dir="ltr">Cliff, I'm not sure how PID loops are implemented on your PLC. My experience is predominately with PACs which are a little more versatile, albeit more expensive. In any case, you don't necessarily have to filter your process variable if it is noisy, as long as the center of the noise band is properly representative of the measurement. Another alternative is to apply rate limiting to the PID output. What loop rate does your PID calculate at? For O2 addition, you probably don't need a strongly responsive system. If the existing control is meeting expectations, I wouldn't mess with it. I was just worried that you had no margin for error.</p>
<p dir="ltr">Sean<br></p>
<br><br><div class="gmail_quote">On April 29, 2017 11:24:42 AM MDT, Cliff Redus via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<pre class="k9mail">Sean, I misspoke, I went back and looked at my PLC ladder logic and it<br />turns out that I turn on the O2 when the concentration drops below 20% and<br />turn off the controller when it goes above 22%. So the control is between<br />20-22 not 18-23. Attached is a graph showing the O2 concentration in<br />automatic O2 makeup mode. You can see that the average O2 in the boat when<br />in Automatic O2 makeup mode is about 21%.<br /><br />[image: Inline image 1]<br /><br /><br />You do make a good point about an alternative strategegy which is to use a<br />PID controller with the set point set being 20.9%. I have many spare PID<br />controller loops avaiblle in the PLC cpu so it would be an easy change in<br />implement. Part of the hesidancy to change was that the sytem as designed<br />is working fine. Also it kind of comforting to hear and see the O2 turn<br />on during the makeup cycle. Part of me says '*if it ain't broke don't fix<br />it*', and
another part of me likes to tinker. I have some noise around the<br />O2 sensor reading. To implement this signal as part of a PID control loop<br />I would need to do some filtering of the O2 concentration measurement to<br />remove some the noise. In the initial setup of the AMOC unit, I had a O2<br />solenoid valve where the comptroller now sits. I replaced the O2 makeup<br />solenoid mainly because I wanted to measure the O2 rate and was able to<br />fine a very nice O2 controller / rate sensor on ebay for next to nothing.<br />So right now I am just sending the controller a high and low signal to make<br />it duplicate a solenoid valve on and off but it would work just as well and<br />maybe better in a PID control loop as the control variable. After I get<br />back from the Islamorada trip, I may set up a test of using PID control of<br />O2 makeup just to see how it compares. With the system as now designed.<br /><br />Thanks for the thoughts.<br /><br />On Sat, Apr
29, 2017 at 8:16 AM, Sean T. Stevenson via<br />Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #729fcf; padding-left: 1ex;"> Cliff, I am curious as to why you are cycling the O2 between the<br /> permissible limits, instead of attempting to maintain the environment at<br /> 20.9% continuously? The latter control scheme provides some safety margin<br /> in that a decrease or rise in O2 level is indicative of a possible problem<br /> well before you fall outside of the limits. If you allow a decline to 18%<br /> or rise to 23% by design, you're already in alarm if anything goes wrong at<br /> either limit. If it is a matter of frequency of valve cycling, perhaps<br /> setting control thresholds at something like 19.25 and 21.75 would permit<br /> the cyclic control while still allowing some detection and response time<br /> before alarming?<br /><br /> Sean<br
/><br /><br /> On April 27, 2017 8:46:52 PM MDT, Cliff Redus via Personal_Submersibles <<br /> personal_submersibles@psubs.org> wrote:<br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #ad7fa8; padding-left: 1ex;"><br /> Brian, the diagram below shows the arrangement I have for life support. I<br /> bring HP (2000 psi) O2 into the Air Management Oxygen Control (AMOC) unit.<br /> The AMOC unit has a pressure reducing regulator that drops the pressure to<br /> about 10 psig. The O2 this passes into a O2 mass meter/controller when in<br /> Automatic mode or through an adjustable needle valve in manual mode. There<br /> a manual O2 variable area, float meter to see O2 rate in SLM. A PLC talks<br /> to the AMOC unit to control O2 supplied into the cabin. Also in the AMOC<br /> box are all the life support sensors, CO2 concentration, O2 concentration,<br /> Relative Humidity, O2 tank pressure, O2 makeup rate, Cabin temperature and<br
/> Cabin pressure. When O2 concentration drops below 18%, PLC tells the<br /> controller to open and deliver O2 at a rate of 4 SLM. When the O2<br /> concentration reaches 23% the PLC turns off the controller. This cycle is<br /> repeat every 30 - 60 m!<br /> inutes<br /> depending on the pilot.<br /><br /> Cliff<br /><br /> [image: Inline image 1]<br /><br /> [image: Inline image 2]<br /><br /> On Thu, Apr 27, 2017 at 9:25 PM, Brian Cox via Personal_Submersibles <<br /> personal_submersibles@psubs.org> wrote:<br /><br /> Cliff, Do you reduce your incoming O2 with a regulator off the O2<br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #8ae234; padding-left: 1ex;"> bottle? Then come in with lower pressure into the cabin?<br /><br /> Brian<br /><br /> --- personal_submersibles@psubs.org wrote:<br /><br /> From: Cliff Redus via Personal_Submersibles <personal_submersibles@psubs.<br /> org><br /> To: Personal
Submersibles General Discussion <personal_submersibles@psubs.<br /> org><br /> Subject: Re: [PSUBS-MAILIST] Co2 scrubbers<br /> Date: Thu, 27 Apr 2017 17:36:51 -0500<br /><br /> Alec if you keep reading down just below the section you site in the<br /> "Oxygen Hackers Companion", y!<br /> ou will<br /> note that the author says "Stainless<br /> steels are used extensively in HP O2 systems ..." "CGA specifies that<br /> valves for O2 tanks should be make of either brass or SS. NASA has<br /> researched this issue (SS for O2 service) and does not reject SS<br /> exclusively.<br /><br /> I use O2 clean SS 1/4" tubing and Swagelok SS valve and fittings for all<br /> my O2 service on my boat . If you O2 clean the systems and use approved O2<br /> lubricants and O-rings, then you, in my mind, have removed the "fuel" leg<br /> of the "Combustion Triangle(fuel, oxidizer and ignition source). If you<br /> are then careful to mitigate adiabatic compression by slow
transfer rates<br /> of less than 60 psi/min, then in my mind you have reduced the risk<br /> associated with adiabatic heating in HP O2 to an acceptable level.<br /><br /> I for one am not going to rip out all my SS O2 tubing and valves and<br /> replace them with brass. In my mind there is certain level of risk<br /><br /> associated with this psubs, O2 fires in O2 clean SS tubing is like risk<br /> level 97 out of 100! Given the rough handling O2 lines and tanks can get,<br /> I would be more afraid of O2 leakage caused by the use of soft tubing and<br /> fittings than the combustion issues sited above.<br /><br /> I went back an looked at the pictures I took from the 2009 Vancouver Psub<br /> convention in Phil's shop. All tubing and valves I could see where SS.<br /><br /> Cliff<br /><br /> On Thu, Apr 27, 2017 at 12:43 PM, Alec Smyth via Personal_Submersibles <<br /> personal_submersibles@psubs.org> wrote:<br /><br /> Here Hank, I'm going to re-type a
couple paragraphs from the Oxygen<br /> Hackers Companion...<br /><br /> Best,<br /><br /> Alec<br /><br /> -----------------<br /> For metal parts, brass is definitely the metal of choice when it comes to<br /> HP O2. It doesn't spark and doesn't (for all practical purposes) burn.<br /> Also, being very thermally conductive, brass can!<br /> add an<br /> extra measure of<br /> safety by acting as a heat sink, to dampen the effects of adiabatic heating<br /> - a recent study has suggested that oversized brass fittings on hoses made<br /> of other materials used with HP O2 can significantly lessen the chance of<br /> combustion, by soakin gup excess heat. Aluminum and titanium are definitely<br /> out - they ignite easily and burn violently in the presence of HP O2. Steel<br /> is not a good choice either - it burns, as anyone who has ever used a<br /> cutting torch knows. But the big problem with steel is that is sparks so<br /> readily, making it a prime potential
source of ignition. SS falls somewhere<br /> in between. While it doesn't spark or burn nearly as easily as steel, it is<br /> not completely immune. The catch is, even good brass fittings are often<br /> rated for only 1500-2000 psi, (100-133 bar), and rarely for more than 3000<br /> psi or so (200 bar). For higher pressure systems, then, there really isn't<br /> !<br /> any<br /> affordable choice but stainless steel, and just about everyone uses it.<br /> It's hard to get a definitive answer on how suitable SS really is for HP<br /> O2.<br /><br /> .. blah, blah..<br /><br /> When it comes to the Oxygen Index, which measures the pressure of oxygen<br /> necessary to sustain combustion once the metal has been ignited, brass is<br /> light years ahead of everything else, at in excess of 10,000 psi (666 bar).<br /> Stainless steel falls in the 500-1000 psi range, with 316 being the worse,<br /> mild steel 100-200 psi, aluminum 25 psi - and titanium 1-2 psi!<br /><br />
.. blah, blah..<br /><br /> The problem is, the soft parts can act as kindling, to ignite the metal<br /> parts, and the metal parts, once burning, can create a major conflagration,<br /> one that is just about impossible to put out. Selecting metal parts that<br /> resist combustion can create a second level of defense against runaway<br /> combustion.<br /> ------------------<br /><br /> On<br /> Thu, Apr 27, 2017 at 12:28 PM, hank pronk via Personal_Submersibles <<br /> personal_submersibles@psubs.org> wrote:<br /><br /> Hmmm, you guys have me worried now. I have a regular steel penetrator for<br /> HP O2, what am I missing. If you can pipe HP O2 through a ss pipe then<br /> why the special bronze? I see O2 regulators that are chrome, not bronze.<br /> I just clean the heck out of the penetrator and I hook er up. Gamma just<br /> had a steel penetrator for HP O2 as well.<br /> Hank<br /><br /><br /> On Thursday, April 27, 2017 10:15 AM, James Frankland
via<br /> Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br /><br /><br /> Hi Brian<br /><br /> I just made it as per the plans. It fits through a stainless insert<br /> welded into the hull. I hadnt put the threads on in this pic. Have a<br /> look at the drawing, you can see where they will go. one each end for the<br /> valve fittings and a thread on the main body for the nut !<br /> to hold<br /> it in.<br /> probably makes it look longer than it is.<br /><br /> I didn't have an issue getting the material. I just ordered from a<br /> standard metal supplier in UK.<br /> Was quite expensive though.<br /><br /><br /><br /> On 27 April 2017 at 16:51, Brian Cox via Personal_Submersibles <<br /> personal_submersibles@psubs.org> wrote:<br /><br /> James, that seems like a very elongated fitting, why does it need to be<br /> so long? Was it hard to locate the "phosphor bronze" I have a piece of<br /> bronze lying around but I'm
have no idea the grade.<br /><br /> Brian<br /><br /> --- personal_submersibles@psubs. org <personal_submersibles@psubs.org><br /> wrote:<br /><br /> From: James Frankland via Personal_Submersibles <personal_submersibles@psubs.<br /> org <personal_submersibles@psubs.org>><br /> To: Personal Submersibles General Discussion <personal_submersibles@psubs.<br /> org <personal_submersibles@psubs.org>><br /> Subje!<br /> ct: Re:<br /> [PSUBS-MAILIST] Co2 scrubbers<br /> Date: Thu, 27 Apr 2017 10:05:29 +0100<br /><br /> Hi Brian<br /> I only have 1 O2 tank mounted outside. Pic here of the bronze through<br /> hull. Kittredge design but I changed the threads to match my valve<br /> fittings. The valve is phosphor bronze as specified on the plans.<br /> Even though its low pressure O2, I used tungem (whatever that is)<br /> tubing inside for the O2 with is specially for O2 applications. I<br /> like it to be super safe.<br /><br />
http://www.guernseysubmarine. com/extended_files/Page647.htm<br /> <<a href="http://www.guernseysubmarine.com/extended_files/Page647.htm">http://www.guernseysubmarine.com/extended_files/Page647.htm</a>><br /><br /> On 27 April 2017 at 06:26, Brian Cox via Personal_Submersibles<br /> <personal_submersibles@psubs. org <personal_submersibles@psubs.org>><br /> wrote:<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> Alec, So on that bronze fitting, if I was using HP O2 coming into the<br /> cabin I would go from the O2 tank outside with SS tubing , then go to a<br /> bronze thru hull fitting ? Then a shut off valve on the inside ( a</blockquote><br /> needle<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> valve type) and then to my flow meter.<br /><br /> Brian C<br /><br /> ---
personal_submersibles@psubs. org <personal_submersibles@psubs.org></blockquote><br /> wrote:<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"><br /> From: Alec Smyth via Personal_Submersibles <personal_submersibles@psubs.</blockquote><br /> org <personal_submersibles@psubs.org>><br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> To: Personal Submersib!<br /> les<br /> General Discussion<br /> <personal_submersibles@psubs. org <personal_submersibles@psubs.org>><br /> Subject: Re: [PSUBS-MAILIST] Co2 scrubbers<br /> Date: Wed, 26 Apr 2017 21:08:08 -0400<br /><br /> I understand Kittredge used bronze, which is good because it's a material<br /> that is very unlikely to initiate an O2 fire. However, in my case we're<br /> already dealing with low pressure at that point, so SS should be
fine.<br /><br /> Best,<br /><br /> Alec<br /><br /> On Wed, Apr 26, 2017 at 10:22 AM, Brian Cox via Personal_Submersibles<br /> <personal_submersibles@psubs. org <personal_submersibles@psubs.org>></blockquote><br /> wrote:<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"><br /> Alec, When you transition your O2 thru the hull don't you have to<br /> have a bronze fitting as a thru hull fitting?<br /><br /> Brian C<br /><br /> --- personal_submersibles@psubs!<br /> . org<br /> <personal_submersibles@psubs.org></blockquote><br /> wrote:<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"><br /> From: Alec Smyth via Personal_Submersibles <personal_submersibles@psubs.</blockquote><br /> org <personal_submersibles@psubs.org>><br /><br /><blockquote class="gmail_quote" style="margin:
0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> To: Personal Submersibles General Discussion<br /> <personal_submersibles@psubs. org <personal_submersibles@psubs.org>><br /> Subject: Re: [PSUBS-MAILIST] Co2 scrubbers<br /> Date: Tue, 25 Apr 2017 22:25:36 -0400<br /><br /> Yep, I did that on both Snoopy and Shackleton. On Snoopy there is one O2<br /> tank outside, which leads to a 1st stage. From there through the hull</blockquote><br /> and on<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> the inside a pediatric flow regulator. Shackleton has the same thing,</blockquote><br /> except<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> two of everything. Same exact setup as Snoopy except one port and one<br /> starboard, for redundancy. Good news, I have run both of them
several</blockquote><br /> times<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> already and they did not turn into flamethrowers. But I'm quite</blockquote><br /> particular<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> about the cleaning. For instance I got a pair of little O2 pressure</blockquote><br /> gauges<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> but decided not to install them!<br /> because<br /> they didn't arrive bagged. I did</blockquote><br /> my<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> own cleaning (twice) on the LP components per Oxygen Hackers Companion<br /> instructions. The HP side (really just a regulator and a 1st
stage) were<br /> purchased O2 clean.<br /><br /><br /> Thanks,<br /><br /> Alec<br /><br /> On Tue, Apr 25, 2017 at 10:03 PM, Rick Patton via Personal_Submersibles<br /> <personal_submersibles@psubs. org <personal_submersibles@psubs.org>></blockquote><br /> wrote:<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"><br /> Hank,<br /><br /> Yeah I think your situation would be different than what I would be<br /> experiencing. I personally just don't believe that there should be any HP<br /> plumbing inside a one atmosphere vessel but that's just my opinion. Is</blockquote><br /> th!<br /> ere<br /><br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #fcaf3e; padding-left: 1ex;"> anyone else out there that is using a first stage reg on a HP exterio</blockquote></blockquote></blockquote></blockquote></pre></blockquote></div></body></html>